The invention relates to a switchable flap valve with at least one valve plate disposed in a housing part so as to pivot about a longitudinal axis in order to close a valve opening provided in the housing part.
Flap valves are used, for example, for controlling the internal pressure of gas-filled containers. One special application is in impact cushions or so-called air bags for the protection of passengers in a motor vehicle. Such air bags are attached with their open edges to a fixed base which contains a rapidly actuatable gas generating unit for filling the air bag and is affixed to the vehicle. The amount of gas delivered to the air bag can basically be controlled through the gas generating unit. This, however, involves great technical complications. In addition to the given amount of gas and the given capacity of the air bag, and many other parameters, the resultant filling pressure depends also on temperature. On the other hand, the filling pressure is critical to the protective action on the body colliding with the air bag, and the optimum filling pressure depends also on the weight of the body to be protected, and on its velocity at impact. Therefore, there has been no lack of attempts to make the filling pressure of the air bag adjustable both for temperature and for different impacting masses.
GB 2,328,649 A discloses forming defined areas of reduced resistance to rupture in the fabric of the air bag. Upon reaching a predetermined internal pressure, these areas burst, so that a suitable average cushioning of the impacting body is achieved, but this does not take into account individual body weights and accelerations on impact. The bursting performance depends on temperature and on the combination of materials, and is not under time control.
A comparable principle is described in U.S. Pat. No. 5,899,494, in which the bursting areas are defined by a fuse cord intended to open areas of the housing as pressure discharge ports. The activation of the fuse cord is controllable as to time and for different areas, but the melting or burning action in the housing is delayed and uncontrolled. The generation of heat must be carefully controlled in order to avoid other kinds of destruction of the bag fabric. Since on the other hand the burned-out housing part must open reproducibly, the firing power is generally designed to be slightly greater than is necessary for melting through the bag.
EP 0 917 994 discloses providing in the air bag a discharge opening whose cross section is made adjustable by means of a loop arrangement in inverse proportion to the actual internal pressure. Here, too, it is not possible to achieve any time related or acceleration related control of the opening cross section. Only certain areas of the air bag are suitable for positioning and attaching the loop arrangements, which limits the choice of material and the way in which the air bag can be folded.
In EP 0 536 677 B1 and EP 0 800 967, valve arrangements are described, which consist of a slide valve system which is arranged on the base for the air bag. A series of ports opening outward are covered by slide valves which can be pushed out of the covering area by a lever mechanism or a motor drive. The lever mechanism is controlled according to temperature. It is sluggish and requires many mechanical parts. The same applies to the motor drive.
A comparable slide valve system is disclosed in GB 2,306,409 A. Around the inflow opening of the gas generator a rotatable segmented diaphragm is disposed from which the excess gas from the inflation of the air bag can escape. Alternatively, an iris diaphragm can be provided to provide a variable opening cross section. A pyrotechnical piston and cylinder system can be provided to drive the covering means. The mechanical cost of the rotary drive and the guidance of the covering means is very high here, as well.
DE 2 324 571 A1 discloses a flap valve affixed to the air bag base, which is resiliently linked to the base body and produces a variable exhaust port depending on the internal pressure of the air bag.
It is the object of the invention to provide a valve system which can be activated according to the body weight of the occupants of the vehicle, the intensity of the collision and the timing of the impact.
Another object of the invention is to provide an air bag valve system which operates independently of temperature.
It is also an object of the invention to provide an air bag valve system which produces a reproducible opening cross section with great reliability and speed.
Another object of the invention is to provide an air bag valve system which can be constructed with little mechanical complexity and requires less space for installation.
These and other objects of the invention are achieved by providing a switchable flap valve comprising at least one valve plate pivotably mounted in a housing part so that the valve plate can pivot about a longitudinal axis to open or close a valve opening in the housing part, wherein each valve plate carries a resiliently deformable strip element aligned parallel to the longitudinal axis of the valve plate on one side thereof, the strip element having a lateral face which faces an adjacent housing wall or a similar face of a strip element on a second valve plate, and the strip element forming a hollow channel with the adjacent housing wall or strip element face, a latch mechanism which holds a free longitudinal edge of the strip element such that the valve plate is secured in a position in which the valve opening is closed, a pressure generator in communication with at least one end of the hollow channel such that actuation of the pressure generator releases a pressure wave into the hollow channel which deforms the strip element and releases the strip element from the latch mechanism so that the at least one valve plate can pivot to a position in which the valve opening is open.
Due to the design of the flap structures which can turn from a closed position to an open position, it is assured that the desired opening cross section will be reliably established. The strip elements arranged on the valve plate make locking and unlocking possible in a simple manner by resilient deformation. The inclined arrangement of the strip elements in order to form a hollow channel makes it possible to achieve contactless actuation of the valve flaps. The valve flaps can be journaled directly in the bottom of the base for the air bag, so that only the catches for the latch mechanism and the gas generator affect the structural height. The small number of working elements and their simple shape also especially permit the entire flap valve to be produced as a one-piece injection molded part which can be disposed over corresponding openings in the base body. The cross section of the opening can be adapted for individual body weight and impact time requirements by means of a plurality of such individually activated valve flaps.